Add pause/resume for isolates in vmservice/observatory.

runtime/bin/dbg_connection.h

Index: runtime/bin/dbg_connection.h
diff --git a/runtime/bin/dbg_connection.h b/runtime/bin/dbg_connection.h
index 8fd0860a5a57ba1071c1a3de42c9b305c50542c4..7efc3f2eb5e12bafd5620347a4f8d1adf9caf3cd 100644
--- a/runtime/bin/dbg_connection.h
+++ b/runtime/bin/dbg_connection.h
@@ -51,6 +51,11 @@ class DebuggerConnectionHandler {
   // from the client.
   static int StartHandler(const char* address, int port_number);
 
+  // Initializes the parts of the debugger which are needed by the vm
+  // service.  This function should only be called when StartHandler
+  // is not called.
+  static void InitForVmService();
+
   // Called by Isolates when they need to wait for a connection
   // from debugger clients.
   static void WaitForConnection();
@@ -99,6 +104,10 @@ class DebuggerConnectionHandler {
   // a debugger to be attached when that is requested on the command line.
   static dart::Monitor* handler_lock_;
 
+  static bool IsListening() {
+    return listener_fd_ != -1;
+  }
+
   // The socket that is listening for incoming debugger connections.
   // This descriptor is created and closed by a native thread.
   static int listener_fd_;